# What happened/caused these 4 great evolutionary milestones **URL:** \ **Category:** Factual Questions\ **Created:** [June 21, 2018, 1:20pm UTC](https://boards.straightdope.com/t/what-happened-caused-these-4-great-evolutionary-milestones/816503 "2018-06-21T13:20:48Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [June 22, 2018, 9:05am UTC](https://boards.straightdope.com/t/what-happened-caused-these-4-great-evolutionary-milestones/816503/21 "2018-06-22T09:05:14Z")
> [@Wesley\_Clark](#): > > 1. The tripling in human brain size about 1 million years ago. > > \ > > For 4, supposedly climate change was the big cause. An ice age increased the demand for cognitive skills. But also the discovery of fire earlier made nutrition easier to get, as well as made food easier to digest. So our jaw muscles shrank allowing for more room for the brain to grow. About 2M years ago (not 1M years ago), you start to see an increase in brain size in our ancestors. Prior, they had chimp-sized brains of about 400 cc. By about 1M years ago, we see an approximate doubling of that size. As we get to Neanderthals and archaic _H. sapiens_ about 250K years ago, we see our current brain size (or slightly larger) of about 1200 cc. Climate change is a favorite hypothesis for evolutionary changes since a change in the environment is something one expects to cause more rapid evolutionary changes. But we don’t know if “an ice age increased the demand for cognitive skills” is the best explanation for why we have the brain size we do. It’s more likely to be a combination of events that selected for larger brains in our evolutionary line. ---
**Author:** ![Delicious](https://avatars.discourse-cdn.com/v4/letter/d/dbc845/32.png) [@Delicious](https://boards.straightdope.com/u/Delicious)\ **Post date:** [June 22, 2018, 11:21am UTC](https://boards.straightdope.com/t/what-happened-caused-these-4-great-evolutionary-milestones/816503/22 "2018-06-22T11:21:34Z")
For #2, I believe the prevalent theory is that it’s a matter of symbiosis developing and merging two species. For mitochondria for example, maybe they start as little bacteria that specialise in burning food, a big prokaryote specialises in gathering food, they start sticking together and it works out for both, over however many generations, the mitochondria start literally sticking to the big prokaryote then a bit further along, they get absorbed…it’s worked out pretty well for them so far, we’ve each for a few trillion of them inside us. For #1, I believe a wizard did it. ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [June 22, 2018, 2:14pm UTC](https://boards.straightdope.com/t/what-happened-caused-these-4-great-evolutionary-milestones/816503/23 "2018-06-22T14:14:33Z")
> [@SamuelA](#): > > Keep in mind that evolution is primarily an algorithm that optimizes towards **local maxima**. Out of the possibility space of all the ways you could organize matter to make a living system, evolution can only search the very nearby regions of this multi-dimensional space. This has to do with probability and the chance of survival with a given mutation. > > What this _means_ is a big part of our existence was due to luck. It was _not_ inevitable. Evolution could have remained stuck on the dinosaurs or some other stable ecology until the star ran out of fuel. Dawkins’ _Climbing Mount Improbable_ is a nice overview of this aspect of evolution, I think. ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [June 22, 2018, 2:17pm UTC](https://boards.straightdope.com/t/what-happened-caused-these-4-great-evolutionary-milestones/816503/24 "2018-06-22T14:17:41Z")
> [@Weisshund](#): > > Why would you want to or need to mold genesis to anything? > probably needs its own thread, but seems a silly thing to do with something that doesnt need molded No, no, [the molds came](https://en.wikipedia.org/wiki/Prototaxites) _after_ the Cambrian. 😃 ---
**Author:** ![am77494](https://avatars.discourse-cdn.com/v4/letter/a/d2c977/32.png) [@am77494](https://boards.straightdope.com/u/am77494)\ **Post date:** [June 22, 2018, 3:53pm UTC](https://boards.straightdope.com/t/what-happened-caused-these-4-great-evolutionary-milestones/816503/25 "2018-06-22T15:53:02Z")
The correct answer is “we don’t know”. Everything else is “scienceplaning”. 🙂 ---
**Author:** ![Drunky\_Smurf](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/drunky_smurf/32/449_2.png) [@Drunky\_Smurf](https://boards.straightdope.com/u/Drunky_Smurf)\ **Post date:** [June 23, 2018, 5:22am UTC](https://boards.straightdope.com/t/what-happened-caused-these-4-great-evolutionary-milestones/816503/26 "2018-06-23T05:22:13Z")
> [@Darren\_Garrison](#): > > There are honestly any number of issues with the speculations in this post, [but this is probably the easiest to address](https://en.wikipedia.org/wiki/RNA_world). (Note the not being DNA.) After reading that link I have a question. Why does RNA and DNA or whatever other chemical chain, that might have existed back then that we don’t know about, “want” to replicate? Is it just a chemical reaction that ends up making a copy? ---
**Author:** ![septimus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/septimus/32/410_2.png) [@septimus](https://boards.straightdope.com/u/septimus)\ **Post date:** [June 23, 2018, 8:12am UTC](https://boards.straightdope.com/t/what-happened-caused-these-4-great-evolutionary-milestones/816503/27 "2018-06-23T08:12:41Z")
> [@Drunky\_Smurf](#): > > After reading that link I have a question. > > Why does RNA and DNA or whatever other chemical chain, that might have existed back then that we don’t know about, “want” to replicate? Is it just a chemical reaction that ends up making a copy? When a single strand of RNA is immersed in a bath containing the right chemicals, there will be a tendency for a complementary strand to form, with the C,G,A,U nucleotides attracted to G,C,U,A nucleotides respectively. If the resultant double strand cleaves into two strands, the original and a complementary strand, a replication has occurred. Repeat and get four strands: two like the original, two complementary. Thus RNA has some tendency to replicate itself. With, say, 100 nucleotides each chosen from {G,C,U,A} there are 4[sup]100[/sup] (about 10[sup]60[/sup]) possible strands. Each possibility would coil into a particular shape, slightly different from others. Each strand, if it replicated at all, would tend to produce its exact complement. _ **That tendency is so weak** _ that catalysts (molecules with just the right shape to facilitate strand formation and cleavage) would be required for the replication to be likely. A particular RNA strand might have the precise shape required for it to catalyze its own replication. [Wikipedia has an article on this](https://en.wikipedia.org/wiki/RNA_world#RNA_as_an_enzyme) — researchers stumbled upon a “189 base pair ribozyme [which] could polymerize a template of at most 14 nucleotides in length, which is too short for self replication, but is a potential lead for further investigation.” (I wonder if such RNA could operate in “teams” with strand[sub]X[/sub] catalyzing the replication of strand[sub]Y[/sub] and vice versa.) Imagine a world with a chemical bath such that RNA strands form randomly. By chance one of these strands might have the shape required to catalyze its self-replication. Naturally that particular RNA would “procreate” profusely, while “eating” the other RNA precursors! Voilà!! ---
**Author:** ![Isilder](https://avatars.discourse-cdn.com/v4/letter/i/cc9497/32.png) [@Isilder](https://boards.straightdope.com/u/Isilder)\ **Post date:** [June 23, 2018, 9:10am UTC](https://boards.straightdope.com/t/what-happened-caused-these-4-great-evolutionary-milestones/816503/28 "2018-06-23T09:10:25Z")
> [@crowmanyclouds](#): > > The [MYH16 gene](https://en.wikipedia.org/wiki/MYH16_gene) mutation. > > CMC fnord! its weakly linked to brain size. The other primates have this gene working, producing high strength muscles and have really strong jaws that can bite through your arm. (no human has bitten through a mans arm bone.). But humans don’t have a working copy of gene MYH16, and don’t have such extremely strong jaws ,and have large brains. There’s no suggestion that the proteins produced by MYH16 poisons large brains, because it doesn’t poison smaller brains, it makes no sense. The change to have defective MYH16 would seem to have created a longer lived, more food efficient primate , because it had less protein problems, which then evolved to travel further to get the food it can’t get from the larger food items because it can’t bite into it. To travel further for food, it evolved to travel more efficiently, and jumping a long like a frog wouldn’t do, and to maintain the agility of the primates, it stood up for longer and longer periods, and moved more while standing up , rather than evolving back to being four legged and running like a gazelle or deer. So when standing up, the skull ceased being used as a battering ram, and the cooling mechanism of the skull/outside of the head evolved to work better, allowing a larger brain inside it ? ---
**Author:** ![Drunky\_Smurf](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/drunky_smurf/32/449_2.png) [@Drunky\_Smurf](https://boards.straightdope.com/u/Drunky_Smurf)\ **Post date:** [June 23, 2018, 4:38pm UTC](https://boards.straightdope.com/t/what-happened-caused-these-4-great-evolutionary-milestones/816503/29 "2018-06-23T16:38:48Z")
> [@septimus](#): > > When a single strand of RNA is immersed in a bath containing the right chemicals, there will be a tendency for a complementary strand to form, with the C,G,A,U nucleotides attracted to G,C,U,A nucleotides respectively. If the resultant double strand cleaves into two strands, the original and a complementary strand, a replication has occurred. Repeat and get four strands: two like the original, two complementary. Thus RNA has some tendency to replicate itself. With, say, 100 nucleotides each chosen from {G,C,U,A} there are 4[sup]100[/sup] (about 10[sup]60[/sup]) possible strands. Each possibility would coil into a particular shape, slightly different from others. Each strand, if it replicated at all, would tend to produce its exact complement. > > _ **That tendency is so weak** _ that catalysts (molecules with just the right shape to facilitate strand formation and cleavage) would be required for the replication to be likely. A particular RNA strand might have the precise shape required for it to catalyze its own replication. [Wikipedia has an article on this](https://en.wikipedia.org/wiki/RNA_world#RNA_as_an_enzyme) — researchers stumbled upon a “189 base pair ribozyme [which] could polymerize a template of at most 14 nucleotides in length, which is too short for self replication, but is a potential lead for further investigation.” (I wonder if such RNA could operate in “teams” with strand[sub]X[/sub] catalyzing the replication of strand[sub]Y[/sub] and vice versa.) > > Imagine a world with a chemical bath such that RNA strands form randomly. By chance one of these strands might have the shape required to catalyze its self-replication. Naturally that particular RNA would “procreate” profusely, while “eating” the other RNA precursors! Voilà!! Neat! Thank you so much. (Ok, I’m putting things in quotes because I know I am not talking precisely and I am trying to dumb it down so my brain will understand.) Ok, I’m taking what you said, and the wiki link, to mean that a certain “chemical” if “properly formed and shaped” will naturally replicate itself due to chemical reactions a percentage of the time. So, and maybe this is off-topic, but “why” would such a complicated chemical bath, such as an animal, aka human being, “want” to replicate? Is it because we are just chemicals ruled by those chemicals to a certain extent? ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [June 23, 2018, 5:02pm UTC](https://boards.straightdope.com/t/what-happened-caused-these-4-great-evolutionary-milestones/816503/30 "2018-06-23T17:02:12Z")
They don’t “want” to do anything. They just do. It is like asking why raindrops want to fall. A physical property of the universe is that a glob of water in an atmosphere under gravity will fall. A physical property of the universe is that some molecules have a shape that allows them to make copies of themselves. No wanting involved. However, once you _do_ have a molecule that can copy itself, natural selection takes over, favoring slight changes in the structure of the molucule that lead to even faster/more often copies of the molecule and the road towards life has started. ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [June 23, 2018, 5:07pm UTC](https://boards.straightdope.com/t/what-happened-caused-these-4-great-evolutionary-milestones/816503/31 "2018-06-23T17:07:17Z")
> [@Darren\_Garrison](#): > > They don’t “want” to do anything. They just do. It is like asking why raindrops want to fall. A physical property of the universe is that a glob of water in an atmosphere under gravity will fall. A physical property of the universe is that some molecules have a shape that allows them to make copies of themselves. No wanting involved. > > However, once you _do_ have a molecule that can copy itself, natural selection takes over, favoring slight changes in the structure of the molucule that lead to even faster/more often copies of the molecule and the road towards life has started. I think **Drunky** was asking why an animal, like a human, would be motivated to reproduce. The answer, of course, is that sex is fun. Why is sex fun? Presumably those animals with the mutation for “fun sex” had more offspring than those without it. ---
**Author:** ![Drunky\_Smurf](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/drunky_smurf/32/449_2.png) [@Drunky\_Smurf](https://boards.straightdope.com/u/Drunky_Smurf)\ **Post date:** [June 23, 2018, 5:33pm UTC](https://boards.straightdope.com/t/what-happened-caused-these-4-great-evolutionary-milestones/816503/32 "2018-06-23T17:33:22Z")
> [@John\_Mace](#): > > I think **Drunky** was asking why an animal, like a human, would be motivated to reproduce. The answer, of course, is that sex is fun. Why is sex fun? Presumably those animals with the mutation for “fun sex” had more offspring than those without it. Yeah, this. After this thread, my past education, and lots of reading on Wiki, I get why chemicals react. Because they do. And sometimes that reaction makes a copy. Given enough time and the right conditions we are here. And as I have been thinking and **John Mace** said, to put it simply, it is, because mutation, and so it is. I guess, I’m just trying to grasp, “Why does life “want” to life?” “Why” do these particular atoms and molecules “want” to make more? Is it really just as simple as, "because that is what they naturally do because of the laws of physics, (or whatever natural laws that govern those things)? And if so, basically, that life is inevitable, given enough time and the right conditions? ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [June 23, 2018, 6:02pm UTC](https://boards.straightdope.com/t/what-happened-caused-these-4-great-evolutionary-milestones/816503/33 "2018-06-23T18:02:56Z")
> [@Drunky\_Smurf](#): > > I guess, I’m just trying to grasp, “Why does life “want” to life?” > > “Why” do these particular atoms and molecules “want” to make more? > > Is it really just as simple as, "because that is what they naturally do because of the laws of physics, (or whatever natural laws that govern those things)? Pretty much. Life no more “wants” to exist than interstellar gas clouds “want” to collapse into solar systems. And since life comes from non-life, how could non-life “want” to be life? > [@](#): > > And if so, basically, that life is inevitable, given enough time and the right conditions? If the universe is infinite, yes. However, as long as we have only a single example of life, that on Earth, we can’t really say what the actual probability is. Life appears in Earth not too long after the crust cooled enough to permit it to exist. There are two interpretations of this fact: 1. The origin of life is easy, and it will develop very quickly whenever the appropriate chemical and physical conditions exist. 2. Life on Earth originated somewhere else, and was seeded here by organisms carried on meteorites that came from impacts on other planets from much older solar systems (the Panspermia hypothesis). This would allow life billions of years more time in which to have originated. The origin of life may be extremely rare, but once it originates it can spread from solar system to solar system. ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [June 23, 2018, 8:59pm UTC](https://boards.straightdope.com/t/what-happened-caused-these-4-great-evolutionary-milestones/816503/34 "2018-06-23T20:59:19Z")
It is all about the copies–if in the “RNA World” a slight change in the sequence means an RNA chain is able to make more copies, then that chain is going to outproduce less productive chains and replace them in the competition for limited resources. the same goes for every level of complexity–any change that leads to producing more seccessful copies will tend to replace ones that don’t. Obviously, having a brain wired to want sex is more likely to lead to sex than a brain that isn’t wired to want sex. ---
**Author:** ![Drunky\_Smurf](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/drunky_smurf/32/449_2.png) [@Drunky\_Smurf](https://boards.straightdope.com/u/Drunky_Smurf)\ **Post date:** [June 24, 2018, 5:19am UTC](https://boards.straightdope.com/t/what-happened-caused-these-4-great-evolutionary-milestones/816503/35 "2018-06-24T05:19:49Z")
Neat. Thanks for the replies. ---
**Author:** ![septimus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/septimus/32/410_2.png) [@septimus](https://boards.straightdope.com/u/septimus)\ **Post date:** [June 24, 2018, 6:47am UTC](https://boards.straightdope.com/t/what-happened-caused-these-4-great-evolutionary-milestones/816503/36 "2018-06-24T06:47:17Z")
The question of why life “wants” to proliferate reminds me of mankind’s transition from hunting/gathering/fishing to farming. It is often supposed that man “wanted” to adopt the more productive economy. But that may be backwards: Hunting/gathering/fishing is fun! — certainly more fun than the tedium of cereal farming. (Many modern people hope to retire so they can take up … hunting, gathering and fishing!) No. Man switched, on balance, to the economy that allowed higher population simply because the hunters, whether _happier_ than the farmers or not, were _out-numbered_ by them. . ---
**Author:** ![Novelty\_Bobble](https://avatars.discourse-cdn.com/v4/letter/n/a3d4f5/32.png) [@Novelty\_Bobble](https://boards.straightdope.com/u/Novelty_Bobble)\ **Post date:** [June 24, 2018, 9:34am UTC](https://boards.straightdope.com/t/what-happened-caused-these-4-great-evolutionary-milestones/816503/37 "2018-06-24T09:34:17Z")
> [@Drunky\_Smurf](#): > > I’m just trying to grasp, “Why does life “want” to life?” > > “Why” do these particular atoms and molecules “want” to make more? These particular atoms and molecules are just a small subset of all the potential chemical combinations (billions and billions and billions) that have occurred over the course of the earth’s existence. It should not be a surprise that those which are able to combine in such a way as to replicate are the ones which we now see as “special” for the creation and evolution of life. I suspect that it is a case of having certain chemicals under certain conditions at a certain time. Try billions of combinations on billions of of billions planets in billions of galaxies over (perhaps) billions of universal cycles and self-replicating chemicals might arise. Only on the one speck of dust where this finally happens can you then get a discussion wondering _why_ this has happened. To reiterate what has been said before though, sometimes “why” is not a valid question as it suggests a degree of conscious reasoning. Often it is better to ask “how” and explore the mechanism. ---
**Author:** ![Drunky\_Smurf](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/drunky_smurf/32/449_2.png) [@Drunky\_Smurf](https://boards.straightdope.com/u/Drunky_Smurf)\ **Post date:** [June 25, 2018, 6:23am UTC](https://boards.straightdope.com/t/what-happened-caused-these-4-great-evolutionary-milestones/816503/38 "2018-06-25T06:23:46Z")
First off, thank you for the replies. 🙂 > [@septimus](#): > > No. Man switched, on balance, to the economy that allowed higher population simply because the hunters, whether _happier_ than the farmers or not, were _out-numbered_ by them. > . So it seems like what **John Mace** said then, “The answer, of course, is that sex is fun. Why is sex fun? Presumably those animals with the mutation for “fun sex” had more offspring than those without it.” Basically, Natural Selection. We do what our ancestors did, and because of that, we do. > [@Novelty\_Bobble](#): > > These particular atoms and molecules are just a small subset of all the potential chemical combinations (billions and billions and billions) that have occurred over the course of the earth’s existence. It should not be a surprise that those which are able to combine in such a way as to replicate are the ones which we now see as “special” for the creation and evolution of life. > > I suspect that it is a case of having certain chemicals under certain conditions at a certain time. Try billions of combinations on billions of of billions planets in billions of galaxies over (perhaps) billions of universal cycles and self-replicating chemicals might arise. > > Only on the one speck of dust where this finally happens can you then get a discussion wondering _why_ this has happened. So, basically, chemicals are going to do what they naturally do and given enough time and the right conditions, viola, I’m here asking, “So, why do they do, to make a me, asking why they do”? (And please remember I am trying to dumb it way the way down in as simple language as I can think of so that I can explain it to my brain.) > [@](#): > > To reiterate what has been said before though, sometimes “why” is not a valid question as it suggests a degree of conscious reasoning. Often it is better to ask “how” and explore the mechanism. I guess that is what I am kind of getting at. I understand chemicals will react because that is what chemicals do, they react. And that explains the “how”? But, also, why does such a complicated bath of chemicals as a person, “want” to make another person. My cells are already using energy and chemicals for replicating and making more copies of themselves to replace damaged and old ones to keep me alive. Why does my chemical bath want to make a whole other being? Does it just go back to natural selection and what **John Mace** said? I mean, as far as we know, is it just that simple? We do, because the ancestors did, and so we do? We’re just a bunch of performing ding dongs following a genetic script? ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [June 25, 2018, 10:22am UTC](https://boards.straightdope.com/t/what-happened-caused-these-4-great-evolutionary-milestones/816503/39 "2018-06-25T10:22:34Z")
The whole and entire “purpose” of organisms is to make more organisms. We (humans, but also junipers, volvox, elephants, slime molds, and shiitake mushrooms) are just complex chemical systems that DNA has developed for producing more DNA. ---
**Author:** ![Nava](https://avatars.discourse-cdn.com/v4/letter/n/da6949/32.png) [@Nava](https://boards.straightdope.com/u/Nava)\ **Post date:** [June 25, 2018, 11:50am UTC](https://boards.straightdope.com/t/what-happened-caused-these-4-great-evolutionary-milestones/816503/40 "2018-06-25T11:50:11Z")
> [@Drunky\_Smurf](#): > > Is it really just as simple as, "because that is what they naturally do because of the laws of physics, (or whatever natural laws that govern those things)? Life is chemistry; chemistry is electricity. Your mom and your pa paired because of electrons, 'cept there is a lot of more levels one can place between “of” and “electrons”. [Previous page](https://boards.straightdope.com/t/what-happened-caused-these-4-great-evolutionary-milestones/816503.md?page=1) [Next page](https://boards.straightdope.com/t/what-happened-caused-these-4-great-evolutionary-milestones/816503.md?page=3)